(1) Field of the Invention
This invention relates to the formation of synthetic polymers from phenols and more particularly, to the formation of polyphenylene oxides by the oxidative coupling of phenols using a particular copper-amine complex to effect the reaction.
(2) Description of the Prior Art
Polyphenylene oxides, sometimes known as poly(phenylene oxides) or as polyphenylene ethers, as a general class, are an extremely interesting group of new polymers. These polymers, both homopolymers and copolymers, and processes of producing them are disclosed in my U.S. Pat. Nos. 3,306,874, 3,306,875 and 3,432,466. Modifications of the process of producing these polymers are described in U.S. Pat. Nos. 3,384,619-Hori et al, 3,639,656-- Bennett et al, 3,642,699, 3,661,848 and 3,733,299-- Cooper et al. All of these patents are hereby incorporated by reference.
The process of my U.S. Pat. No. 3,306,875 involves the self-condensation of a monovalent phenol using a catalyst comprising a tertiary amine-basic cupric salt complex. Both polymers and diphenoquinones are products of this reaction depending on the reaction conditions and the phenols used. Under the polymer-forming conditions the phenols which can be oxidatively coupled to polymers have the structural formula: ##STR1## where X is a hydrogen, chlorine, bromine or iodine; Q is hydrogen, hydrocarbon radicals, halohydrocarbon radicals having at least 2 carbon atoms between the halogen atom and the phenol nucleus, hydrocarbonoxy radicals and halohydrocarbonoxy radicals having at least two carbon atoms between the halogen atom and the phenol nucleus; and Q' and Q" are the same as Q and in addition, halogen with the proviso that Q, Q' and Q" are all free of a tertiary .alpha.-carbon atom.
The polymers formed by this reaction will have the formula: ##STR2## where the oxygen atom of one repeating unit is connected to the phenylene nucleus of the next repeating unit; Q,Q' and Q" are as defined above; and n is a number representing the average degree of polymerization and is at least 100, if the polymer is to have good molding and film-forming properties.
The formation of the polyphenylene oxide involves an oxidative-coupling of the phenol using as the oxygen carrying intermediate, a tertiary amine-basic cupric salt complex. Except for those phenols which are so sterically hindered that they can only form diphenoquinones, the products of the reaction are a mixture of diphenoquinones and polyphenylene oxides, with the ratio of these two products being dependent upon the reaction conditions used. Reaction conditions can be so chosen that either polyphenylene oxides or diphenoquinones are produced with only a very small amount of the corresponding other product. My U.S. Pat. No. 3,306,874 is similar to 3,306,875 except that primary and secondary amines are used in place of tertiary amines, and a more limited class of phenols must be used as the starting material.
The Hori U.S. Pat. No. 3,384,619 also relates to a process for preparing polyphenylene oxides from phenols. By using a very high ratio of certain specific tertiary amines, typically 10 moles of amine per mole of phenol, and relatively high copper to phenol ratios, typically 0.1 moles of copper per mole of phenol, complexes of non-basic cupric salts with the tertiary amine can be used to effect the polymerization reaction, providing the reaction is carried out in a solvent system containing at least 5 weight percent of a low molecular weight alcohol. The above ratio of 10 moles of tertiary amine per mole of phenol, on a weight basis, means that 8 grams of even a low molecular weight amine such as triethylamine is required per gram of 2,6-xylenol.
The process disclosed in the Bennett et al U.S. Pat. No. 3,639,656 is an improvement over the Hori et al process. It is based upon using a complex of a primary or secondary amine with an anhydrous non-basic cupric salt which permits using a smaller amount of this complex, with relation to the phenol than Hori et al and also eliminates the use of the alcohol. Typically 0.01 mole of copper and 0.15 mole of amine is used per mole of phenol.
The Cooper et al U.S. Pat. No. 3,642,699 discloses the use of a cuprous salt complex of a primary, secondary or tertiary amine to which a low molecular weight alkyl alcohol is added prior to the addition of the phenol reactant. In this way the alcohol forms a part of the catalyst. In their U.S. Pat. No. 3,661,848, Cooper et al disclose that by forming the cupric salt complex of a primary or secondary amine in the presence of a low molecular weight alkyl alcohol, copper salts can be used in their hydrate form and even aqueous solutions of the copper salt can be used to form the complex. In both of these patents the moles of copper and amine per mole of phenol are similar to those of the Bennett et al patent.
The Cooper et al U.S. Pat. No. 3,733,299 discloses that an alkali metal bromide or alkaline earth metal bromide acts as an activator for the cupric or cuprous salt complexes of primary, secondary or tertiary amines used to oxidatively couple phenols to polyphenylene oxides. The amines which can be used are the same as those disclosed in my U.S. Pat. Nos. 3,306,874 and 3,306,875. Although this activation by bromide permits the reduction of the amount of copper to 0.0033 mole per mole of phenol, the amount of amine is still typically .15 mole per mole of phenol.